There's no mandate (that I know of), but there is a strong culture of dogfooding that tends to push one to using IE. There's also many intranet sites that won't

There's no mandate (that I know of), but there is a strong culture of dogfooding that tends to push one to using IE. There's also many intranet sites that won't work without ActiveX. But certainly no one's dropped by my office to ask me to stop using my alternate browser (I tend to separate my usage by my usage patterns. Work stuff on IE, personal stuff on the non-IE browser).